Modified carrier, complex oxide catalyst and process for preparation of acrylic acid

ABSTRACT

A modified carrier carrying on at least a part of an inert carrier surface an oxide which is represented by the formula (1): X a Y b Z c O d  (wherein X is at least an element selected from alkaline earth metals; Y is at least an element selected from Si, Al, Ti and Zr; Z is at least an element selected from Group IA elements and Group IIIb elements of the periodic table, B, Fe, Bi, Co, Ni and Mn; and O is oxygen; a, b, c and d denote the atomic ratios of X, Y, Z and O, respectively, where a=1, 0&lt;b≦100, 0≦c≦10, and d is a numerical value determined by the extents of oxidation of the other elements) is provided. A catalyst formed with the use of this modified carrier carrying a complex oxide containing Mo and V is useful as a vapor-phase catalytic oxidation catalyst, and is particularly suitable as a catalyst for preparing acrylic acid through vapor phase catalytic oxidation of acrolein.

FIELD OF INDUSTRIAL UTILIZATION

[0001] This invention relates to catalyst carrier, complex oxidecatalyst and production process of acrylic acid. More particularly, theinvention relates to a modified carrier suitable as a carrier of acatalyst for making acrylic acid from acrolein by vapor phase catalyticoxidation reaction, a catalyst formed by supporting a complex oxidecatalyst on said modified carrier, and to a producing process of acrylicacid using said catalyst.

PRIOR ART

[0002] A large number of improved catalysts for preparing acrylic acidthrough vapor phase catalytic oxidation reaction of acrolein have beenproposed. For example, Japanese Patent Publication No. 12129/69described a catalyst formed of molybdenum, vanadium and tungsten;Publication No. 11371/74, that formed of molybdenum, vanadium, copper,tungsten and chromium; Publication No. 25914/75, that formed ofmolybdenum and vanadium; and Laid-open (Kokai) Patent Application, KokaiNo. 85091/77, that formed of molybdenum, vanadium, copper and at leastone element of antimony and germanium.

[0003] However, these conventional catalysts are not fully satisfactoryfor industrial working, because of such defects that the yield of theobject product, i.e., acrylic acid, is insufficient and deteriorationrate in activity is high, leading to short catalyst life. Therefore,development

[0004] of catalysts which excel in stability and enable acrylic acidproduction at high yield over prolonged periods has been in demand.

[0005] [Problem to be Solved by the Invention]

[0006] Accordingly, one of the objects of the present invention is toprovide a carrier, in particular, a novel carrier suitable for use inproduction of acrylic acid through vapor phase catalytic oxidation ofacrolein.

[0007] Another object of the invention is to provide a complex oxidecatalyst, in particular, a complex oxide catalyst which is suitable forproducing acrylic acid through vapor phase catalytic oxidation ofacrolein.

[0008] A further object of the present invention is to provide a processfor preparing acrylic acid at high yield over prolonged periods, byoxidizing acrolein in the presence of catalyst at vapor phase withmolecular oxygen or a molecular oxygen-containing gas.

[0009] [Means to Solve the Problem]

[0010] We have discovered that a product obtained by having a commonlyused inert carrier carry an oxide containing at least an elementselected from alkaline earth metals, at least an element selected fromsilicon, aluminum, zirconium and titanium, and optionally at least anelement selected from Group IA elements and Group IIIb elements of theperiodic table, boron, iron, bismuth, cobalt, nickel and manganese on atleast a part of its surface (which product is hereafter referred to as amodified carrier) is useful as a carrier of the oxidation catalyst; andthat the use of, for example, a product which is obtained by having themodified carrier carry a complex oxide containing molybdenum andvanadium (which product is hereafter referred to as a complex oxidecatalyst) as the catalyst in the oxidation reaction of acrolein enablesproduction of acrylic acid in high yield stably over prolonged periods.

[0011] Thus, according to the invention, a modified carrier is provided,which is characterized in that an inert carrier is caused to carry, onat least a part of its surface, an oxide expressed by the formula (1):

X_(a)Y_(b)Z_(c)O_(d)  (1)

[0012] (where X is at least an element selected from alkaline earthmetals, Y is at least an element selected from silicon, aluminum,titanium and zirconium, Z is at least an element selected from Group IAelements and Group IIIb elements of the periodic table, boron, iron,bismuth, cobalt, nickel and manganese, and O is oxygen; a, b, c and ddenote the atomic ratios of X, Y, Z and O, respectively; and where a=1,0<b<100 (preferably 0.01≦b≦100), 0≦c≦10, and d is a numerical valuedetermined by the extents of oxidation of the other elements).

[0013] According to the invention, also a complex oxide catalystcharacterized by having a complex oxide containing molybdenum andvanadium, in particular, a complex oxide which is expressed by thefollowing general formula (2):

Mo_(e)V_(f)W_(g)Cu_(h)A_(i)B_(j)O_(k)  (2)

[0014] (where Mo is molybdenum, V is vanadium, W is tungsten, Cu iscopper, A is at least an element selected from antimony, niobium andtin, B is at least an element selected from phosphorus, tellurium, lead,arsenic and zinc, and O is oxygen; e, f, g, h, i, j and k denote atomicratios of Mo, V, W, Cu, A, B and O, respectively; and where e is 12,2≦f≦15, 0≦g≦10, 0<h≦6 (preferably 0.01≦h≦6), 0≦i≦6, 0≦j≦5, and k is anumerical value determined by the extents of oxidation of the otherelements),

[0015] carried on said modified carrier is provided.

[0016] According to the invention, furthermore, a process forpreparation of acrylic acid by oxidizing acrolein at vapor phase withmolecular oxygen or a molecular oxygen-containing gas in the presence ofa catalyst is provided, the process being characterized by the use ofsaid complex oxide catalyst as the catalyst.

[0017] [Embodiments of the Invention]

[0018] As the inert carrier, any of those generally used for preparationof various catalysts, in particular, catalysts for oxidation ofacrolein, can be used, the typical ones being silica, alumina,silica-alumina, silicon carbide, silicon nitride, titanium dioxide,zirconium oxide and the like. Of those alumina and silica-alumina arethe preferred.

[0019] The modified carrier of the invention is formed by having such aninert carrier carry on at least a part of its surface an oxiderepresented by the general formula (1). That is, the modified carrier ofthe invention is formed of an inert carrier and an oxide of the generalformula (1) which is carried on at least a part of the surface of theinert carrier. The form of the oxide of the general formula (1) which iscarried on the inert carrier is subject to no critical limitation, butit is normally preferred that an effective amount of the oxide coversthe inert carrier with an approximately uniform thickness.

[0020] The amount of the oxide of the general formula (1) which is to becarried on the inert carrier is such that can at least exhibitsufficient carriage effect. More specifically, it is satisfactory tohave the inert carrier support thereon an oxide of the general formula(1) at a carriage ratio of 1-50%, preferably 3-30%, said ratio beingcalculated by the following equation:

carriage ratio (%)=[1−(weight of inert carrier/weight of modifiedcarrier)]×100.

[0021] Where the carriage ratio is less than 1%, the effect of themodified carrier cannot be sufficiently obtained. Whereas, when itexceeds 50%, the surface properties of the inert carrier itself such ascoarseness and porosity are impaired by the supported oxide, to reduceadhesion between the modified carrier and the catalytic componentsupported thereon, giving rise to such a problem as peel-off of thecatalyst component.

[0022] The condition of carriage of the oxide of the general formula (1)on the inert carrier surface in the modified carrier of the inventioncan be confirmed by means of a linear or planar analysis ofcross-section with EPMA (Electron Probe Micro Analyzer).

[0023] Among the oxides which are expressed by the general formula (1),those whose X-component is magnesium, calcium, strontium or barium;Y-component is silicon or aluminum; Z-component is sodium, potassium,iron, cobalt, nickel or boron; and where a=1, 0<b≦100 (preferably0.01≦b≦100) and 0≦c≦10, are preferred.

[0024] The modified carrier of the invention can be prepared followingthe general by practiced methods for having an inert catalyst carry thesubstance to be supported. For example, compounds containing at least anelement selected from alkaline earth metals; at least an elementselected from silicon, aluminum, zirconium and titanium; and optionallyat least an element selected from Group IA elements and Group IIIbelements of the periodic table, boron, iron, bismuth, cobalt, nickel andmanganese are supported and deposited on an inert carrier, in such aform of an aqueous solution, suspension or powder by such means asimpregnation, spraying or evaporation to dryness, and if necessarydried, and heat-treated at a temperature range of 500° C.-2,000° C.,preferably 700° C.-1,800° C., inter alia, 800° C.-1,700° C., for around1-10 hours. Obviously, it is permissible to use, as one of the startingcompounds, a compound concurrently containing X-component andY-component.

[0025] The complex oxide catalyst of the invention is a catalyst formedby carrying on said modified carrier a complex catalyst comprisingmolybdenum and vanadium, preferably a complex oxide which is expressedby the earlier given general formula (2). Such a complex oxide catalystcan be prepared in the manner generally practiced for preparing thiskind of complex oxide catalysts, excepting that the modified carrier isused. For example, it can be prepared by such a method in which thestarting compounds are deposited on the modified carrier and thereafterconverted to the complex oxide by calcination.

[0026] Among the complex oxides which are expressed by the generalformula (2), those whose A-component is antimony or tin, B-component isphosphorus, tellurium and zinc; and where a 32 12, 2≦f≦15, 0≦g≦10, 0<h≦6(preferably 0.01≦h≦6), 0≦i≦6 and 0≦j≦5 are preferred.

[0027] Shapes of the modified carrier and the complex oxide catalyst ofthe invention are not critical. Any optional forms such as ring, sphere,column and the like can be selected. The average diameter as thecatalyst is 1-15 mm, preferably 3-10 mm.

[0028] Suitable amount of the complex oxide containing molybdenum andvanadium to be supported on the modified carrier is 10-70%, preferably15-50%, in terms of the supported ratio (%) as calculated by thefollowing equation:

supported ratio (%)=[(weight of the complex oxide)/(weight of themodified carrier)+(weight of the complex oxide)]×100

[0029] In preparing complex oxide catalyst of the invention, those wellknown additives having the effect of improving the strength andattrition resistance of catalysts; such as inorganic fibers, e.g., glassfiber or various whiskers may be added. Also for controlling physicalproperties of the catalyst with good reproducibility, additives such asammonium nitrate, cellulose, starch, polyvinyl alcohol, stearic acid andthe like may be used.

[0030] The complex oxide catalyst of the invention is obtained uponcalcining the catalyst precursor as deposited on the modified carrier at300° C.-600° C., preferably at 350° C.-500° C., for about 1-10 hours.

[0031] The acrylic acid production process of the invention can becarried out following any of generally practiced methods for producingacrylic acid through vapor phase oxidation of acrolein, except that theabove-described complex oxide catalyst is used. Therefore, the apparatusand operating conditions in carrying out the production are notcritical. That is, as the reactor, an ordinary fixed bed reactor,fluidable bed reactor or moving bed reactor can be used, and thereaction can be carried out under the conditions conventionally employedfor production of acrylic acid from acrolein through vapor phasecatalytic oxidation reaction. For example, a gaseous mixture of 1-15volume % of acrolein, 0.5-25 volume % of oxygen, 1-30 volume % of steamand 20-80 volume % of an inert gas like nitrogen, is contacted with acomplex oxide catalyst of the invention at temperatures ranging from 200to 400° C., under a pressure of 0.1-1 MPa and at a space velocity of300-5,000 h⁻¹ (STP) to produce acrylic acid.

[0032] Besides such gaseous mixtures of acrolein, oxygen and inert gas,acrolein-containing gaseous mixtures which are obtained through directoxidation of propylene may also be used as the starting gas, ifnecessary after adding air or oxygen and steam. Presence of such sideproducts as acrylic acid, acetic acid, carbon oxide and propane orunreacted propylene in the acrolein-containing gaseous mixtures obtainedupon direct oxidation of propylene is in no way detrimental to thecomplex oxide catalyst used in this invention.

[0033] [Effect of the Invention]

[0034] According to the invention, high-activity and high-performancecatalysts are obtainable with good reproducibility. Moreover, becausethe complex oxide catalysts of the invention maintain the high activitylevels over prolonged periods, acrylic acid can be stably produced athigh yields over prolonged periods according to the process of theinvention.

EXAMPLES

[0035] Hereinafter the invention is explained more specificallyreferring to working Examples, it being understood that the Examplesincur no restricting effect on the invention.

[0036] In the Examples, the acrolein conversion, acrylic acidselectivity and acrylic acid yield were calculated according to thefollowing equations:

acrolein conversion (%)=[(mol number of reacted acrolein)/(mol number offed acrolein)]×100

acrylic acid selectivity (%)=[(mol number of formed acrylic acid)/(molnumber of reacted acrolein)]×100

acrylic acid yield (%)=[(mol number of formed acrylic acid)/(mol numberof fed acrolein)]×100

Example 1

[0037] [Preparation of a Modified Carrier Formed of an Inert CarrierCarrying an Oxide (Mg—Si—Al)]

[0038] Into 2,000 ml of pure water, 890 g of magnesium nitrate and 130 gof aluminium nitrate were dissolved under heating and stirring. Into theformed solution, 1563 g of 20 weight % silica sol was added and mixed,followed by addition of 2,000 g of silica-alumina spherical carrier of 5mm in average particle diameter as an inert carrier. The system wasevaporated to dryness under heating. Subsequently the heatingtemperature was raised stagewisely. Upon calcination at 1,300° C. for 3hours at the final stage, a modified carrier [modified carrier (1)] wasobtained. The composition of the carried oxide (excepting oxygen, likein all of the following compositions) was as follows:

Mg₁Si_(1.5)Al_(0.1).

[0039] The carriage ratio was 18.3%.

[0040] [Preparation of Complex Oxide Catalyst]

[0041] Into 2,000 ml of pure water, 350 g of ammonium paramolybdate,96.6 g of ammonium metavanadate and 44.6 g of ammonium paratungstatewere dissolved under heating and stirring. Separately, 87.8 g of cupricnitrate and 4.8 g of antimony trioxide were added to 200 g of pure waterunder heating and stirring. Thus obtained two liquids were mixed andtogether poured into a porcelain evaporator on hot water bath. Then,1,200 ml of the modified carrier (1) was added, followed by evaporationto dryness under stirring to have the catalyst deposited on the modifiedcarrier (1). The carrier-supported catalyst was calcined at 400° C. for6 hours to provide a complex oxide catalyst [Catalyst (1)]. Thecomposition of metallic elements (excepting oxygen, as in all ofhereafter indicated compositions) of this Catalyst (1) was as follows:

Mo₁₂V₅W₁Cu_(2,2)Sb_(0.5).

[0042] The supported ratio was 22%.

[0043] [Oxidation Reaction]

[0044] A stainless steel reaction tube of 25 mm in diameter was chargedwith 1,000 ml of thus obtained Catalyst (1), and into which a gaseousmixture of 5 volume % of acrolein, 5.5 volume % of oxygen, 25 volume %of steam and 64.5 volume % of inert gas comprising nitrogen and the likewas introduced. The reaction was carried out at 260° C. and at a spacevelocity (SV) of 1,500 h⁻¹ (STP). The catalyst performance at theinitial period and after 8,000 hours' reaction was as shown in Table 1.

Comparative Example 1

[0045] Catalyst (2) was prepared in the identical manner with thecatalyst preparation in Example 1, except that the inert carrier wasused as it was. The oxidation reaction was carried out under identicalconditions with those of Example 1, except that the Catalyst (2) wasused. The result was as shown in Table 1.

Example 2

[0046] [Preparation of a Modified Carrier Formed of an Inert CarrierCarrying an Oxide (Ca—Ba—Si)]

[0047] Into 2,000 ml of pure water, 8.2 g of calcium nitrate, 9.1 g ofbarium nitrate and 1.5 g of sodium nitrate were dissolved under heatingand stirring. To this solution 563 g of 20 weight % silica sol was addedand mixed, and into the liquid mixture 2,000 g of silica-aluminaspherical carrier having an average particle diameter of 5 mm was addedas an inert carrier, followed by evaporation to dryness under heating.The heat-treating temperature was raised stagewisely. Upon 5 hours'calcination at 1,400° C. at the final stage, a modified carrier[modified carrier (2)] was obtained. The composition of the carriedoxide was as follows:

(Ca_(0.5)Ba_(0.5))₁Si₂₇Na_(0.25).

[0048] The carriage ratio was 5.4%.

[0049] [Preparation of a Complex Oxide Catalyst]

[0050] A complex oxide catalyst [Catalyst (3)] was prepared in theidentical manner with Example 1, except that the modified carrier (1)was replaced with the modified carrier (2).

[0051] [Oxidation Reaction]

[0052] The reaction was carried out under identical conditions withthose in Example 1, except that Catalyst (1) was replaced with Catalyst(3). The result was as shown in Table 1.

Example 3

[0053] [Preparation of a Modified Carrier Formed of an Inert CarrierCarrying an Oxide (Mg—Si—Al)]

[0054] Into 2,000 ml of pure water, 1423 g of magnesium nitrate, 112 gof iron nitrate, 5.6 g of potassium nitrate and 208 g of aluminiumnitrate were dissolved under heating and stirring. The solution wasmixed with 2500 g of 20 weight % silica sol, and into the liquid mixture2,000 g of silica-alumina spherical carrier having an average particlediameter of 5 mm was added as an inert carrier, followed by evaporationto dryness under heating. Thereafter the heat-treating temperature wasraised stagewisely, and upon 3 hours' calcination at 1,200° C. at thefinal stage, a modified carrier [modified carrier (3)] was obtained. Thecomposition of the carried oxide was as follows:

Mg₁Si_(1.5)Al_(0.1)K_(0.01)Fe_(0.05).

[0055] The supported ratio was 27%.

[0056] [Preparation of Complex Oxide Catalyst]

[0057] A complex oxide catalyst [Catalyst (4)] was prepared in theidentical manner with the catalyst preparation in Example 1, except thatthe modified carrier (3) was used in place of the modified carrier (1).

[0058] [Oxidation Reaction]

[0059] The reaction was carried out under identical conditions withthose in Example 1, except that Catalyst (1) was replaced with Catalyst(4). The result was as shown in Table 1.

Example 4

[0060] [Preparation of a Modified Carrier Formed of an Inert CarrierCarrying an Oxide (Sr—Si—Al)]

[0061] Into 2,000 ml of pure water, 183.6 g of strontium nitrate and 650g of aluminium nitrate were dissolved under heating and stirring. Thesolution was mixed with 625 g of 20 weight % silica sol, and into theliquid mixture 2,000 g of a silica-alumina spherical carrier having anaverage particle diameter of 5 mm was added as an inert carrier,followed by evaporation to dryness under heating. The heat-treatingtemperature was raised stagewisely, and upon 3 hours' calcination at1,500° C. at the final stage, a modified carrier [modified carrier (4)]was obtained. The composition of the carried oxide was as follows:

Sr₁Si_(2.4)Al₂.

[0062] The carriage ratio was 12.6%.

[0063] [Preparation of a Complex Oxide Catalyst]

[0064] A complex oxide catalyst [Catalyst (5)] was prepared in theidentical manner with the catalyst preparation in Example 1, except thatthe modified carrier (4) was used in place of the modified carrier (1).

[0065] [Oxidation Reaction]

[0066] The reaction was carried out under identical conditions withthose in Example 1, except that Catalyst (1) was replaced with Catalyst(5). The result was as shown in Table 1.

Example 5

[0067] [Preparation of a Modified Carrier Formed of an Inert CarrierCarrying an Oxide (Mg—Si)]

[0068] Into 2,000 ml of pure water, 300 g of magnesium silicate(manufactured by Nakarai Tesque Co.) was added, and further 2,000 g ofsilica-alumina spherical carrier having an average particle diameter of5 mm was added as an inert carrier, followed by evaporation to drynessunder heating. Thereafter the heat-treating temperature was raisedstagewisely, and upon 2 hours' calcination at 1,700° C. at the finalstage, a modified carrier [modified carrier (5)] was obtained. Thecomposition of the carried oxide was as follows:

Mg₁Si_(1.5).

[0069] The carriage ratio was 9.7%.

[0070] [Preparation of a Complex Oxide Catalyst]

[0071] A complex oxide catalyst [Catalyst (6)] was prepared in theidentical manner with the catalyst preparation of Example 1, except thatthe modified carrier (5) was used in place of the modified carrier (1).

[0072] [Oxidation Reaction]

[0073] The reaction was carried out under identical conditions withthose in Example 1, except that Catalyst (1) was replaced with Catalyst(6). The result was as shown in Table 1. TABLE 1 Reaction AcroleinAcrylic Acid Acrylic Catalyst Temp. conversion Selectivity Acid YieldNo. (° C.) (%) (%) (%) Example 1 (1) Initial stage of reaction 260 99.296.0 95.2 After 8,000 hrs. 270 99.2 95.8 95.0 Comparative (2) Initialstage of reaction 260 98.4 94.4 92.9 Example 1 After 8,000 hrs. 287 98.693.9 92.6 Example 2 (3) Initial stage of reaction 260 99.0 95.4 94.4After 8,000 hrs. 271 99,0 95.3 94.3 Example 3 (4) Initial stage ofreaction 260 99.3 95.9 95.2 After 8,000 hrs. 269 99.2 95.7 94.9 Example4 (5) Initial stage of reaction 260 99,1 95.6 94.7 After 8,000 hrs. 27099.0 95.5 94.5 Example 5 (6) Initial stage of reaction 260 99.0 95.194.1 After 8,000 hrs. 273 99.1 95.0 94.1

1. A modified carrier which is characterized by carrying on at least apart of an inert carrier surface an oxide expressed by the formula (1):X_(a)Y_(b)Z_(c)O_(d)  (1) (wherein X is at least an element selectedfrom alkaline earth metals; Y is at least an element selected from agroup consisting of silicon, aluminum, titanium and zirconium; Z is atleast an element selected from a group consisting of Group IA elementsand Group IIIB elements of the periodic table, boron, iron, bismuth,cobalt, nickel and manganese; and O is oxygen; a, b, c and d denote theatomic ratios of X, Y, Z and O, respectively, and where a=1, 0<b≦100 and0≦c≦10, and d is a numerical value determined by the extents ofoxidation of the other elements).
 2. A modified carrier as described inclaim 1, in which the inert carrier is selected from a group consistingof silica, alumina, silica-alumina, silicon carbide, silicon nitride,titanium dioxide and zirconium oxide.
 3. A complex oxide catalyst whichis characterized by supporting a complex oxide containing molybdenum andvanadium on the carrier as described in claim
 1. 4. A complex oxidecatalyst as described in claim 3, in which the complex oxide containingmolybdenum and vanadium is a complex oxide which is expressed by thefollowing general formula (2):Mo_(e)V_(f)W_(g)Cu_(h)A_(i)B_(j)O_(k)  (2) (where Mo is molybdenum, V isvanadium, W is tungsten, Cu is copper, A is at least an element selectedfrom a group consisting of antimony, niobium and tin; B is at least anelement selected from a group consisting of phosphorus, tellurium, lead,arsenic and zinc, and O is oxygen; e, f, g, h, i, j and k denote atomicratios of Mo, V, W, Cu, A, B and O, where a=12, 2≦f≦15, 0≦g≦10, 0<h≦6,0≦i≦6, 0≦j≦5, and k is a numerical value determined by the extents ofoxidation of the other elements).
 5. A process for preparing acrylicacid through oxidation of acrolein at vapor phase with molecular oxygenor a molecular oxygen-containing gas in the presence of a catalyst,which is characterized in that the complex oxide catalyst of claim 3 or4 is used as the catalyst.